The present invention is a vibration damper system for any tennis racket or ball-game racket, made from flexible and rigid thermoplastic or thermosetting material that is inserted between the strings or onto the frame of a ball-game racket. The system absorbs the vibrations of the stringing and the frame that are caused by the impact of the ball.
The state of the previous techniques is given here in detail, in order to understand the technological progress made by the present invention. It is a well-known fact that an element made of elastomer or thermoplastic placed onto the strings of a racket absorbs the vibrations in the stringing. Lacoste""s French patent no 1.308.833, filed in 1964, presented a vibration damper made from flexible material in the form of a toric shape, with grooves to fix it onto the stringing of the racket. Then, other systems arrived to perfect the Lacoste patent, such as the German patent DE 34 43 009 A 1, filed in 1984, and DE 35 04 137 A1, filed in February 1985. Both of these patents present systems that were made from elastomer, also toric shaped like in Lacostes patent, and which used a metallic mass creating a perpendicular oscillation over the plane of the stringing whilst the elastomer of the toric is flexible. According to the hardness of their elastomer parts, and the space between the strings of the racket, the systems oscillate at different frequencies.
Indeed, if the strings are spaced apart, the central part of the elastomer on which the metallic mass is attached is more flexible. As a result, the oscillations of the mass occur at a lower frequency. If the strings are closer together, the opposite occurs, i.e. the mass oscillates at a higher frequency. Since it is the oscillations of the metallic mass in phase with the vibrations of the racket that determine the efficiency of the vibration damper, these systems are not universal. The U.S. Pat. No. 5,651,545, based on the German patents mentioned above, proposes to change the metallic masses according to the frequencies that are required. The French patent no 2.585.257 filed in July 1985 is, again, a toric form with a counterweight, associated with a membrane system that is supposed to transmit the vibrations. However, beyond the fact that the movement of the counterweight is, inevitably, very small, the membrane connecting the said counterweight to the elastomer toric is compressed to a varying extent, depending on the spacing of the strings, and so the system is unable to efficiently absorb vibrations in all types of rackets. All of the systems known until now that comprise of a flexible element and a metallic mass oscillate very little, because the oscillation is always perpendicular to the plane of the racket stringing Therefore, their efficiency is limited, and only the vibrations of one type of racket, with a particular spacing of the strings, can be absorbed. None of the systems is intrinsically adjustable to oscillate in phase with the vibrations to be dampened in the racket. The present invention overcomes these drawbacks. In the first, preferred version, the invented device comprises of at least two elements. The first, in a compact form, made from a flexible material, is inserted between the strings of the racket, in the same way as in the Lacoste patent no 1.398.833 referred to above; the other element is more rigid, and is inserted inside, or fixed outside the flexible element, perpendicular to two strings of the racket. This second element comprises of a perpendicular protrusion, positioned between the two strings and pointing along the longitudinal axis of the said strings. When a ball hits the stringing, the resulting vibrations induce a perpendicular protrusion to move, causing the second element to rotate and dissipate the vibrations. Thus, the elastic pressure of the first elastomer element on the second, more rigid element, is constant, whatever the spacing of the strings. The frequency of the motion of the rotating part is identical, whatever the spacing of the strings, because its semi-rigid articulation is disconnected from the oscillations of the flexible element, which themselves are perpendicular to the stringing.
The movable, rotating part turns around its central axis, inserted into the flexible element. To avoid the system from coming detached from the stringing, the more rigid element has, at each end, an upper and lower protrusion, between which the strings are positioned. Eveni if the rotation of the rigid part is rather limited, the movement of the extremity of the protrusion is always much greater, and the system is attached perfectly to the strings. To accentuate the rotating effect of the rigid element, the protrusion of this element contains a metallic part with a hole, into which the more rigid part is inserted, which slots in between the strings. By adjusting the semi-rigid articulation with a twisting movement, the oscillation frequency can by set by rotating the movable element to the frequency of vibrations to be dampened. For this purpose, the movable part features a strip made from a semi-rigid material, close to the centre of rotation, that itself is articulated to rotate around the axis of the plane of the stringing, which overlaps the flexible elastomer adjacent to the first element. So, when the strip is positioned along the axis of the movable element, the resistance to bending of the latter, brought about by the compact flexible element inserted between the cords, remains unchanged.
But if the user, by rotating the strip, manually positions the strip perpendicularly to the movable part, that is by overlapping the first flexible element over the sides, the rigidity of the semi-rigid articulation of the movable part increases. Thus, depending on the position of the strip, the rotation frequency of the movable part can be modified and can be adapted more accurately to the frequency of vibration of the racket, to dampen the vibrations more efficiently. A variant uses a strip that slides along a rail, positive or negative, positioned on the visible surface of the movable element, parallel to its longest sides The strip is then positioned perpendicular to the longest sides of the movable element. By sliding the strip along the rail placed on the movable part, the extremities of the strip overlap the adjacent elastomer part, located on both sides of the movable element, and the rigidity of the semi-rigid articulation of the movable part is modified. By simple positioning the strip, the system can be adjusted perfectly to the vibrations that need to be dampened. Another variant allows the additional mass to be moved forwards or backwards in relation to the axis of rotation of the movable element. In this case, the said movable element includes a rail, onto which the additional mass is positioned. If the additional mass is inside the movable element, its housing is larger than the additional mass to be housed. The housing is pulled in parallel along the length of the movable element, i.e. in an eccentric direction in relation to the movable element. When the additional the axis of rotation of the movable element. In this case, the said movable element includes a rail, onto which the additional mass is positioned. If the additional mass is inside the movable element, its housing is larger than the additional mass to be housed. The housing is pulled in parallel along the length of the movable element, i.e. in an eccentric direction in relation to the movable element. When the additional mass moves closer or further from the centre of rotation, the movable element reduces or increases the vibration frequency of the movable element, enabling a precise adjustment of the vibration frequency to the vibration frequency of the racket to be dampened. In another variant of the system the elastomer element is fixed to the frame of the racket, which has a protrusion onto which the more rigid rotating part is fixed, with a hollow and/or an additional mass to increase the inertia of the said rigid element.